Factors Affecting Fuel System Certification Against Lightning Hazards

The certification of fuel systems is an important aspect of the overall certification of an aircraft against lightning hazards and embraces almost all disciplines needed to deal with the lightning interaction. Both direct and indirect effects are encountered and some understanding of the physics of fuel combustion and probability theory concerning ignition is also necessary to appreciate the factors influencing the safety or otherwise of a design. At one time the Western Air Forces were losing one aircraft every other year, due to lightning related fuel explosions. Similar accidents occur to Civilian aircraft, albeit less frequently. After a brief review of aircraft fuels and their flammability and some discussion of combustion processes, the paper considers factors affecting Minimum Ignition Energy (MIE) encountered during flight profiles, such as oxygen enrichment, temperature and pressure. The paper also reviews possible ignition sources, such as hotspots, thermal and voltage sparking, and stresses the need for a rigorous Lightning Hazard Design Analysis (LHDA) as part of the certification process. Areas that should be included in the LHDA are noted.

The paper reviews Lightning Standards relating to fuel and notes areas where shortcomings are thought to be present.

Mr Tilston is a Principal Consultant at QinetiQ (formerlyDERA) Pyestock with 40 years experience in Combustion and Fuel Technology.